This invention relates to an ink jet recording apparatus comprising a recording head for jetting ink drops from nozzle orifices based on print data, thereby printing on recording paper. Particularly, this invention to an ink jet recording apparatus that can prevent a print failure from occurring by suppressing volatilization of an ink solvent from the recording head during a suspend mode of the recording apparatus in order to avoid the influence of bubbles that can occur due to the surface tension of the ink solvent.
The ink jet recording apparatus is used for various types of print including color print in these days because print noise is comparatively small and moreover small dots can be formed at a high density.
The ink jet recording apparatus comprises an ink jet recording head for receiving ink supplied from an ink cartridge and a paper feeder for moving recording paper relatively to the recording head and jets ink drops onto recording paper for recording while moving the recording head on a carriage in the width direction of the recording paper.
The recording head capable of jetting black ink and color inks of yellow, cyan, and magenta is mounted on the carriage, enabling not only text print in black ink, but also full color print by changing the content percentage of the respective color inks.
Since ink pressurized in pressure generation chambers is jetted to recording paper as ink drops from nozzle orifices for printing, the recording head installed in the recording apparatus involves the problem of causing a print failure to occur because of a rise in the ink viscosity or hardening of ink caused by evaporation of an ink solvent from the nozzle orifices, deposition of dust, mixing of bubbles into an ink flow passage, or the like.
Thus, this kind of ink jet recording apparatus comprises a capping unit for sealing the nozzle formation face of the recording head in non-print mode (suspend mode) and a wiping member for wiping out and cleaning the nozzle formation face as required.
The capping unit serves as a lid for preventing ink in the nozzle orifices from being dried in the suspend mode of print; it: can suppress clogging caused by drying ink in the nozzle orifices of the recording head for providing the reliability of the print operation at the restart time of print.
Further, the capping unit also serves as a cleaner unit for sealing the nozzle formation face and sucking and discharging ink from the nozzle orifices by negative pressure generated by a suction pump, thereby resolving an ink jet failure caused by clogging caused by ink hardening in the nozzle orifices or mixing of bubbles into the ink flow passage.
To make the capping unit function effectively as a lid for preventing ink in the nozzle orifices from being dried during quiescent operation of print as described above, the related recording apparatus adopts a control sequence of jetting a predetermined amount of ink into the capping unit from the recording head just before the capping operation.
On the other hand, the capping unit stores an ink absorption material of a porous foam formed like a sheet on the inner bottom of the capping unit formed like a rectangle and ink is held by the ink absorption material, thereby maintaining the internal space of the capping unit in a wet state with the nozzle formation face sealed.
By the way, in addition to a water content, polyhydric alcohol such as glycerine or diethylene glycol as a humectant is mixed in print ink for maintaining the inside of the capping unit in a wet state.
The polyhydric alcohol has a nature of absorbing (retaining) water from the air and is used as an ink solvent to suppress an increase in viscosity of ink and hardening of ink for preventing clogging mainly in the minute nozzle orifices of the recording head.
However, in a state in which the ink absorption material of a porous foam is placed in the capping unit as described above, the water content is evaporated from the ink absorption material with the passage of time, but the above-mentioned humectant is left in the ink absorption material and the composition percentage rises gradually with the passage of the use time of the recording apparatus.
Therefore, if the humectant is left in the ink absorption material in a high composition percentage, it absorbs the water content in the internal space in the capped state of the recording head, developing a problem of drying ink in the nozzle orifices of the recording head.
Focusing attention on the adverse effect of the humectant contained in print ink and from the viewpoint, it is a first object of the invention to provide a structure wherein the ink absorption material placed on the inner bottom of the capping unit is removed and to suck and discharge ink from the recording head, the ink can be discharged promptly so that it is not left in the capping unit, and provide an ink jet recording apparatus comprising a capping unit in which a high-density humectant is not accumulated and moreover an adequately wet state can be maintained by the water content contained in the ink and make it possible to ensure reliability of print of a recording head.
On the other hand, in the structure wherein the ink absorption material placed on the inner bottom of the capping unit is removed, as described above, if sealing of the nozzle formation face of the recording head with the capping unit is released, a large bubble shaped like a so-called soup bubble appears by the surface tension of an ink solvent between the seal face of the capping unit and the nozzle formation face of the recording head; this is a problem.
It is considered that a bubble occurs because a porous member as an ink absorption member does not exist and the inside. of the capping unit is formed as comparatively smooth faces.
FIGS. 33 to 36 schematically show the situation in order. FIG. 33 shows a state in which the nozzle formation face of the recording head is sealed with the capping unit. FIGS. 34 to 36 show with the upper half part shown in FIG. 33 not shown how the above-mentioned large bubble shaped like a so-called soup bubble is left in the capping unit as sealing of the nozzle formation face of the recording head with the capping unit is released.
Identical components shown in FIGS. 33 to 36 are denoted by the same reference numerals.
First, as shown in FIG. 33, a nozzle plate 12a forming a nozzle formation face 12a of a recording head 12 is placed on the bottom face of a head case 12b forming a part of the recording head 12 and is formed with a plurality of nozzle orifices 12c. Actuators 12d, for example, implemented as piezoelectric vibrators are placed in the head case 12b in a one-to-one correspondence with the nozzle orifices 12c. 
Communication channels 12e are formed in the head case 12b from the nozzle orifices 12c and the actuators 12d to the top thereof.
Four hollow ink introduction needles 41 are placed upright on the top of the head case 12b and the communication channels 12e formed in the head case 12b are made to communicate with hollow passages of the ink introduction needles 41.
An ink introduction hole (not shown) is made in the vicinity of the crest of each ink introduction needle 41 and ink from an ink cartridge is introduced through each ink introduction hole into the corresponding ink introduction needle 41 and is supplied via the communication flow passage 12e to the actuator 12d of the recording head 12.
The ink introduction needle 41 at the left end shown in FIG. 33 is provided for receiving black ink and a black ink cartridge 7 is attached toward the ink introduction needle 41 at the left end from the top.
A color ink cartridge 8 stores color inks of cyan, magenta, and yellow separately in order from left to right in FIG. 33 and is also attached toward the three remaining ink introduction needles 41 from the top as shown in FIG. 33.
On the other hand, the capping unit 9 is made up of a holder 21 and a cap member 22 of a rubber material, etc., having an end face formed almost like a square, the cap member 22 being placed on the top face of the holder 21. The holder 21 is housed in a slider 43 that can be moved up and down with a circular art path via a link arm 42.
An engagement projection 9e is placed at an end part of the slider 43 and abuts a part of the head case 12b as a carriage on which the recording head 12 is mounted is moved to the home position side (right in the figure), and the nozzle formation face 12a of the recording head 12 is sealed with the cap member 22 moved up through the link arm 42.
From the seal state of the nozzle formation face 12a with the capping unit 9 shown in FIG. 33, the carriage is moved a little to the print area side (left in FIG. 34) as shown in the figure, whereby the capping unit 9 is moved down through the link arm 42, whereby the sealing of the nozzle formation face 12a with the capping unit 9 is released.
When a slight gap occurs between the nozzle formation face 12a and the capping unit 9, a film Bu is formed in the gap by the surface tension of ink discharged into the capping unit 9.
In the structure of the capping unit 9 shown in the example, if the capping unit 9 is furthermore moved down as shown in FIG. 35, it is inclined a little to the print area side, namely, is brought out of contact with the nozzle formation face 12a in an unparallel state therewith.
Therefore, the film Bu generated by the surface tension of ink solvent is moved in the right direction in the figure where the spacing between the capping unit 9 and the nozzle formation face 12a is narrow, and grows to a large bubble Bu shaped like a so-called soup bubble.
As shown in FIG. 36, the carriage on which the recording head 12 is mounted is further moved to the print area side, whereby the large bubble Bu is left in the capping unit 9.
If the nozzle formation face 12a of the recording head 12 is again sealed in the state in which the large bubble shaped like a soup bubble is thus left in the capping unit 9, the large bubble Bu disappears and at the instant, a meniscus of ink formed in the nozzle orifice is destroyed; this is a problem. Thus, an ink drop cannot normally be jetted through the nozzle orifice, namely, a print failure of a missing dot occurs.
Particularly, in recent years, higher-precision print quality has been required increasingly and there has been a tendency to use ink using a pigment, for example. In such ink using a pigment, the surface tension is comparatively large and particularly bubbles easily occur.
It is therefore a second object of the invention to provide an ink jet recording apparatus for making it possible to avoid a print failure caused by occurrence of a large bubble shaped like a soup bubble or aggressively prevent a large bubble from occurring and an ink composition suited to the ink jet recording apparatus, thereby preventing occurrence of a print failure of a missing dot, etc., and ensuring reliability of print of a recording head.
To accomplish the above-mentioned object, according to the invention, there is provided an ink jet recording apparatus comprising:
a recording head having a nozzle formation face provided with nozzle orifices from which ink drops are jetted to print on a recording medium in accordance with print data;
a capping unit having an internal space communicated with a negative pressure generator, and having an opening for sealing the nozzle formation face and sucking ink from the nozzle orifices into the internal space by negative pressure generated by the negative pressure generator;
an ink discharge port formed on a bottom portion of the internal space of the capping unit; and
an ink leader provided in the capping unit so as to generate capillary action to lead the sucked ink toward the ink discharge port.
Preferably, a pair of slopes are formed in the internal space so as to extend from the opening toward the bottom portion. The ink leader is provided as a valley line defined as an intersection of the slopes. The ink discharge port is formed on a part of the valley line.
In this case, preferably, the opening is formed into a rectangular shape. The valley line extending in a longitudinal direction of the rectangular opening.
Preferably, a groove is formed along the valley line.
Alternatively, the ink leader is provided as a plurality of grooves formed on the bottom portion of the internal space so as to extend toward the ink discharge port.
In this case, preferably, the width of each groove is gradually narrowed toward the ink discharge port.
Alternatively, the ink leader is provided as a plurality of protruded ribs formed on the bottom portion of the internal space so as to extend toward the ink discharge port.
In this case, preferably, the width of each gap defined between the protruded ribs is gradually narrowed toward the ink discharge port.
In the above cases, preferably, water-repellent treatment is applied to surfaces of the internal space.
In the above cases, preferably, a method of discharging ink comprises the steps of:
sealing the nozzle formation face with the capping unit;
driving the negative pressure generator to suck ink from the nozzle orifice into the internal space of the capping unit;
separating the capping unit from the nozzle formation face; and
driving the negative pressure generator to discharge the sucked ink from the ink discharge port such that the discharging speed is controlled such an extent that no suction vortex appears in the sucked ink.
According to the above configurations, the ink sucked into the capping unit is promptly led to the ink discharge port by the ink leader presenting capillary action without remaining in the capping unit.
Therefore, accumulating and gradually leaving the above-mentioned humectant contained in ink in the capping unit at high density can be suppressed and a problem of absorbing and hardening the ink solvent (water content) in the nozzle orifices of the recording head can be circumvented.
In this case, ink discharged from the nozzle orifices can be led more smoothly to the ink discharge port by applying water-repellent treatment to the inner face of the capping unit as described above.
To use the ink discharge method in combination, ink is discharged from the capping unit at low suction speed to such an extent that a suction vortex is not formed on an ink surface above the ink discharge port, thus the liquid level of the ink in the capping unit is uniformly lowered and a little ink last left is also pulled into the ink discharge port by the action of the surface tension and the probability of leaving ink in the capping unit can be decreased drastically.
In order to accomplish the second object more perfectly in addition to the first object, according to the invention, a method of discharging ink comprises the steps of:
sealing the nozzle formation face with the capping unit;
driving the negative pressure generator to suck a first amount of ink from the nozzle orifice into the internal space of the capping unit;
separating the capping unit from the nozzle formation face;
driving the negative pressure generator to discharge the sucked ink from the internal space of the capping unit;
sealing again the nozzle formation face with the capping unit; and
driving the negative pressure generator to suck a second amount of ink, which is smaller than the first amount, from the nozzle orifice in order to restore a meniscus of ink in each of the nozzle orifices.
In order to execute the above method, the ink jet recording apparatus further comprises a controller for causing the negative pressure generator to apply the negative pressure to the ink discharge port in order to:
(1) suck a first amount of ink from the nozzle orifices when the capping unit seals the nozzle formation face;
(2) suck a second amount of ink, which is smaller than the first amount, from the nozzle orifices when the capping unit seals the nozzle formation face; and
(3) suck ink remained in the internal space when the capping unit is apart from the nozzle formation face.
Preferably, the capping unit is separated from the nozzle formation face in an unparallel attitude with respect to the nozzle formation face in accordance with a predetermined movement of the recording head. The ink discharge port is placed at an end portion of the bottom portion of the internal space which is closer to the nozzle formation face when the capping unit starts to be separated from the nozzle formation face.
Alternatively, the capping unit is separated from the nozzle formation face in a parallel attitude with respect to the nozzle formation face in accordance with a predetermined movement of the recording head. A pair of ink discharge ports are placed at both end portions of the bottom portion of the internal space.
Alternatively, the ink jet recording apparatus further comprises a projection for breaking bubbles appearing due to surface tension of an ink solvent.
In this case, preferably, the opening of the capping unit is formed into a rectangular shape. A pair of slopes are formed in the internal space so as to extend from the opening toward the bottom portion such that a valley line defined as an intersection of the slopes extends in a longitudinal direction of the rectangular opening. The projection is formed on each of the slopes.
In the above cases, preferably, an ink composition of the ink contains 0.2-1.5 wt % of a surfactant.
According to the above configurations, ink is sucked from the nozzle orifices of the recording head by executing the cleaning operation, then ink in the capping unit is discharged by the idle suction operation. Then, again the small suction operation of ink from the recording head is executed.
Therefore, a large bubble shaped like a so-called soup bubble appears by the surface tension of ink discharged by the initial suction operation. When capping is again executed, a meniscus of ink in the nozzle orifice is destroyed accordingly, but can be restored to the former state by later executing the small suction operation of ink.
In the executed small suction operation of ink, the remaining ink amount in the capping unit is only a little and therefore the degree of again generating a large bubble shaped like a soup bubble can be lessened extremely.
In the recording apparatus wherein the capping unit is brought out of contact with the nozzle formation face in the unparallel attitude with the nozzle formation face of the recording head, according to the above-described configuration, air in a large bubble shaped like a soup bubble can be positively discharged by executing the suction operation.
Thus, the soup bubble is shrunk and occurrence of a print failure caused by the large bubble can be avoided.
Also in the recording apparatus wherein the capping unit is brought out of contact with the nozzle formation face in an almost parallel attitude with the nozzle formation face of the recording head, according to the above-described configuration, air in a large bubble shaped like a soup bubble can be positively discharged by executing the suction operation. Thus, the soup bubble is shrunk and occurrence of a print failure caused by the large bubble can be avoided.
Further, also in the recording apparatus wherein a projection is formed in the capping unit, a large bubble appearing by the surface tension of an ink solvent can be made to disappear or hard to occur in the presence of the projection, and occurrence of a print failure can be avoided.
In a case where predetermined amount of a surfactant is contained in the ink composition used with the recording apparatus, the degree of generating a large bubble shaped like a soup bubble can be decreased, and occurrence of a print failure can be avoided more efficiently with the synergistic effect with the effect of the above described configurations.
According to the present invention, there also may be adopted a configuration that the capping unit includes a holder member which defines. at least the opening and the bottom portion of the internal space thereof, and a seal member held by the opening, which is to be abutted against the nozzle formation face.
In this case, preferably, the holder member and the seal member are made of materials different with each other.
Preferably, the holder member is made of a synthetic resin material, and the seal member is made of a rubber material.
Alternatively, the holder member includes an inner shell portion which defines the internal space and an outer shell portion integrally formed with the inner shell portion so as to surround the inner shell portion. The seal member is formed between the inner shell portion and the outer shell portion integrally therewith.
In the above cases, preferably, an interior angle between the slopes is 160 degrees or less.
Alternatively, a cross section of the slopes is curved.
In the above cases, a surface roughness of the bottom portion of the internal space is 25 xcexcm or less.
According to the above configurations, ink sucked into the capping unit is smoothly led to the ink discharge port by the ink leader presenting capillary action without remaining in the capping unit.
Therefore, accumulating and gradually leaving the above-mentioned humectant contained in ink in the capping unit at high density can be avoided and a problem of absorbing and hardening the ink solvent (water content) in the nozzle orifices of the recording head can be circumvented.
In this case, ink discharged from the nozzle orifices can be led more smoothly to the ink discharge port by applying water-repellent treatment to the inner face of the capping unit as described above and the inner bottom face of the capping unit has surface roughness set within the above-mentioned numeric value, whereby the remaining degree of ink on the inner bottom face of the capping unit can be furthermore decreased.
Thus, if the interior angle formed by the pair of slopes inclined from the opening of the capping unit to the bottom of the internal space of the capping unit is made comparatively large, the remaining degree of ink on the inner bottom face of the capping unit can be decreased, so that the outer dimensions of the capping unit, particularly the dimension in the height direction can be lessened.
Since the dimension from the opening of the capping unit to the bottom of the internal space is also lessened accordingly, the degree of separating ink into minute drops and changing to fog (ink mist) in the flushing operation of idly jetting ink toward the capping unit can be decreased.
Therefore, the subsidiary effect of making it possible to decrease occurrence of contamination caused by occurrence of the ink mist can also be expected.
On the other hand, since the holder member and the seal member are made of different materials, occurrence of bubbles caused by the surface tension of ink can be decreased because they differ in interfacial state, and the degree of occurrence of a print failure caused by occurrence of a bubble can be decreased.
According to the present invention, there also may be adopted a configuration that the ink leader includes a slope continuously extending from the opening to the ink discharge port, and a liquid retainer formed on a communication path between the ink discharge port and the negative pressure generator.
In this case, preferably, the liquid retainer is provided as a plurality of ribs protruded from an inner face of the communication path.
Alternatively, the liquid retainer is provided as a plurality of grooves formed on an inner face of the communication path.
Alternatively, the liquid retainer is provided as a liquid absorbing member provided at a connecting portion of the ink discharge port and the communication path.
Alternatively, the liquid retainer is provided as a plurality of thin tubes formed in the communication path so as to extend therealong.
In the above cases, preferably, water-repellant treatment is applied to the slope formed in the capping unit and hydrophilic treatment is applied to the liquid retainer.
According to the above configurations, ink sucked from the nozzle orifices flows into the ink discharge port along the smooth slope without accumulating.
When the suction operation is performed by the negative pressure generator, ink is discharged to the outside without being left by the liquid retainer placed in the communication path between the negative pressure generator and the ink discharge port.
Therefore, the problem of accumulating the above-mentioned humectant contained in ink in the internal space of the capping unit at high density can be solved.
Since the liquid retainer placed in the communication path holds ink jetted from the recording head just before the capping time, the water content contained in the ink can maintain the internal space of the capping unit at high humidity and efficiently suppress evaporation of ink in the nozzle orifices.
In this case, the water-repellent treatment is applied to the slope formed from the opening in the capping unit to the ink discharge port, whereby ink jetted from the nozzle orifices can be smoothly led from the slope to the ink discharge port.
The hydrophilic treatment is applied to the liquid retainer placed in the pipe line communicating with the negative pressure generator from the ink discharge port, whereby the ink holding effect of the liquid retainer by the capillary action can be more increased.
That is, to suck and discharge ink from the recording head in the cleaning operation, ink in the capping unit can be discharged reliably. If the flushing operation of applying a drive signal not involved in print to the recording head for idly jetting ink drops to the inside of the capping unit is executed, ink replenished by the flushing operation can be held in the liquid retainer and the water content contained in the ink jetted by the flushing operation can maintain the internal space of the capping unit at high humidity.